X-ray circuit for eliminating grid shadows



Dec. 23, 1941.v A slMoN v 2,267,141 x-RAY CIRCUIT FOR ELIMINITING GRIDsHADows l Filed sept. 14, 1959 ggf/M.

atented Dec. 23, 1941 X-RAY CIRCUIT FOR ELIlVIlNATING GRID SHADOWSAlfred Simon, Jackson Heights, Long Island,

N. Y., assignor, by mesne assignments, to Westinghouse Electric andManufacturing Company, East Pittsburgh, Pa., a corporation ofPennsylvania Application september 14, 1939, serial No. 294,833

(c1. o-c2) 4 Claims.

The present invention relates to X-ray systems and particularly to suchsystems wherein high voltage is employed for the making of radiographicexposures utilizing a Bucky grid and in which grid lines heretoforeappearing on the lm are eliminated.

It has long been recognized in the art that in radiographing solidsubstances such as the human body, secondary radiations are generated bythe primary radiations striking denser portions such as the bones. Toprevent these secondary radiations from fogging a film, it has beencustomary to employ what is known in the art as a Bucky grid which iscomposed of alternate strips of X-ray pervious and impervious material.During exposure, this grid is moved between the object and lm so thatthe grid pattern on the film becomes obliterated.

While the grid eliminates fogging of the lm from secondary radiations,it nevertheless, unless moved during exposure, leaves grid lines on thefilm where the primary rays do not penetrate the X-ray impervioussections, which all to frequently renders the lm exceptionally diiicultto diagnose. It naturally follows that if the X-ray tube is energized bydirect current, no grid lines will appear upon the developed lm when thegrid is uniformly moved during exposure. Since it is exceptionallydicult and frequently impossible due to commercial conditions to obtain.high voltage direct current, it is customary to employ alternatingcurrent as the energizing source which is stepped up by a high voltagetransformer.

Inasmuch as the current and voltage reverse many times a second,depending upon the frequency, and thus pass through zero points of thealternating current wave as well as high points, there are naturallyvery` brief intervals when no X-rays are generated followed by longerperiods when the intensity of the X-rays rises from zero to maximum andagain falls to zero. This rise and fall of the intensity of the X-raysis what causes the registration of the grid lines on the lm with thewidth thereof being dependent upon the difference in time between thefrequency of the alternating current and the speed of movement of thegrid.

Various attempts have been made by workers in the art to eliminate thegrid lines by increasing the speed of movement of the grid. Suchattempts have proven unsuccessful because no practical way has at yetbeen found to make the speed of the grid such that those speeds that arein simple or multiple synchronism with the X-ray frequency are avoidedwhen employing alternating current of commercial frequencies rangingfrom 25 cycles per second to 60 cycles per second, which thus results inthe appearance of grid lines. While prior art workers Vhave beenconcerned with the mechanical requirements of adjusting the speed ofmovement of thegrid, I have discovered that by the proper electricaldesign of the energizing circuit, radiographs can be taken using a Buckygrid and wherein grid lines on the film are eliminated.

It is accordingly the primary object of the present invention to providean X-ray system for the taking of radiographic exposures wherein a Buckygrid is employed to intercept secondary radiations and wherein gridlines on the film .are eliminated.

lAnother object of the present invention is the provision of an X-raysystem of relatively high power for the taking of radiographic exposureswith the utilization of a Bucky grid to eliminate secondary radiationsand wherein the sinusoidal wave form of the alternating current sourceis suppressed so that grid lines are prevented from registering upon theexposed film.

Still further objects of the present invention will become obvious tothose skilled in the art by reference to the accompanying drawingwherein the single gure is a diagrammatic illustration showing thesystem for the taking of radiographic exposures utilizing a Bucky gridin accordance with the present invention. Y

Referring now to the drawing in detail, the system as shown in Fig. 1comprises a high tension transformer 5 having its primary winding 6connected to a suitable source of electrical energy of the customarypotential of or 220 volts as shown by the terminals LI, L2. The highpotential secondarywinding .'I is grounded in the center at 8 and hasone end thereof connected by a conductor 9 to the respective anode andcathodel of a pair of rectifying valve tubes IIl and I2.

Similarly the remaining end of the secondary winding 'I is connected bya conductor I3 to the respective anode and cathode'of another pair ofrectifying Valve tubes I4 and' I5. In order to supply full waverectified unidirectional current to the X-ray tube I6, a conductor I'Iconnects the thermionic cathode of the X-ray tube I6 to the anode of thetwo rectifying valves I2 and I5, while the anode of the X-ray tube isconnected by a conductor I9 to the thermionic cathdes of the otherrectifying Valve tubes Illand The thermionic cathodes of the rectifyingvalves I0, I2, I4 and I5 as well as the thermionic cathode of the X-raytube IB receive heating current from any suitable source such asbatteries, individual low voltage heating transformers or a singletransformer as desired, although such low voltage source has not beenshown in the drawing for the sake of simplicity.

For the purpose of suppressing the usual sinusoidal ripple, such asshown Vby the curve A in Fig. 2 which is characteristic of full waverectified unidirectional current, a pair vof series connected condensers22 and 23 are connected in electrical parallel with the X-ray. tube Vandgrounded at 24. Accordingly, upon connection of the primary winding 6 ofthe high voltage transformer to the customary domestic source ofpotential, a high voltage alternating current is induced in thesecondary winding 'I. The current then flows through one or the other ofthe pairs of rectifying valves during each h alf wave of the alternatingcurrent cycle, thus converting the alternating current intounidirectional current which is supplied to the X-ray tube.

The condensers 22 and 23 having a capacity of approximately .125microfarad each, which may be a single condenser or a bank of condensersof the desired capacity, being in electrical parallel with the X-raytube are accordingly charged and during the periods when the flow ofcurrent is approaching zero the condensers discharge through the X-raytube. The resulting effect is a substantially constant potential whereinthe current falls only about 10% below what it would if true directcurrent were employed, such as shown by the curve B of Fig. 2.

The circuit thus described, wherein a constant potential is employed toenergize an X- ray tube, has been heretofore used in the art inconnection with the administration of therapeutic treatments. So far vasI am aware, the use of high power full wave rectified single phasecurrent of the order of `100 to 300 milliamperes has never been employedfor the taking of radiographic exposures particularly in combinationwith a Bucky grid for the elimination of grid `lines on the film.

By subjecting a patient 25 to the X-ray tube I6 while positioned on atable 25, vand disposing a Bucky grid 21 between the patient and a lm28, and moving the grid while the exposure is made, no grid lines appearon the exposed iilm. For example, I have found from my experiments thatwith a given speed adjustment of the Bucky grid and utilizing a fullwave rectified current varying from 100 to 300 milliamperes withoutconstant potential, the resulting film had the appearance of the gridhaving been stationary, such as shown at C in Fig. 3 wherein the gridlines 29 are immediately discernible. Moreover, the speed of movement ofthe grid was varied and even at the optimum speed, such grid lines werestill quite pronounced. However, by utilizing a high powered constantpotential in combination with the Bucky grid, the lines were completelyeliminated even at the worst speeds of the grid, resulting in a iilmsuch as that shown at D in Fig. 3.

It will thus become obvious to those skilled in the art that anelectrical system is herein provided wherein high powered constantpotential electrical current is utilized to energize an X-ray vtube sothat a Bucky grid may be employed during the exposure to eliminatesecondary radiations and wherein grid lines on the developed film areeliminated.

Although one specific embodiment of the present invention has been shownand described, it is to be understood that further modifications thereofmay be made without departing from the spirit and scope of the appendedclaims.

I claim:

l. In an X-ray system for the taking of radiographic exposures free ofgrid lines, the combination of a Bucky grid for intercepting secondaryradiations and uniformly movable between the object to be radiographedand a sensitized nlm during exposure of the latter, a source of highpower electrical energy and of high constant potential, and an X-raytube connected to said source and operable to generate X-rays ofsubstantially constant intensity for the purpose of eliminating gridlines on said film when exposed to X-rays from said tube and afterpassing through said grid.

2. In an X-ray system for the taking of radiograph-ic exposures free of-grid lines, the combination of a Bucky grid for intercepting secondaryradiations and uniformly movable between the object to be radiographedYand a sensitized film Vduring exposure of the latter, a source of highpower alternating current electrical energy, rectifying means connectedto said source for converting the alternating current into full waveunidirectional current, -means connected to said rectifying means andoperable to suppress the sinusoidal wave form attendant full Waverectified unidirectional current to produce a constant potential, and anY -ray tube connected to both said means for energization by theconstant potential produced by said last mentioned means to cause thegeneration -of X-rays of substantially constant intensity for thepurpose of eliminating grid lines on said film when exposed to X-raysfrom said tube and after passing through said grid.

3. In an X-ray system for the taking of radiographic exposures free ofgrid lines, the combination of Ya Bucky grid for intercepting secondaryradiations and uniformly movable between the object to be radiographedand a sensitized film during exposure -of the latter, a source of highpower alternating current electrical energy comprising a high voltagetransformer vprovided with a secondary winding, -a plurality ofrectifyingvalve tubes connected to said secondary winding for convertingthe alternating current into full wave unidirectional current, capacitor'means connected to said rectifying valve tubes and-operable to suppressthe sinusoidal wave form attendant full wave rectified unidirectionalcurrent to produce a constant potential, and an X- ray tube connected tosaid capacitor means for energization by the constant potential producedthereby to cause the generation of X-rays of substantially constantintensity for the purpose of eliminating grid llines on said fim whenvexposed to X-rays from said tube and after passing through said grid.

4. In an X-ray system for the taking of radiographic exposures free ofgrid lines, the combination of a Bucky grid for intercepting secondaryradiations and uniformly movable between the object to 'be radiographedand a sensitized vfilm during exposure of the latter, a source of highpower alternating current electrical energy comprising 'ahigh'voltage'transformer provided with a secondary winding, al'plurality of rectifying valve tubes connected to said secondarywinding for converting the alternating current into full waveunidirectional current, a bank of condensers of a predetermined capacityconnected to said rectifying valve tubes and operable to suppress thesinusoidal Wave form attendant full Wave rectied unidirectional currentto produce a constant potential, and an X-ray tube connected to saidrectifying Valve tubes and in electrical parallel with said condensersfor energization by the constant potential produced thereby to cause thegeneration of X-rays of substantially constant intensity for the purposeof eliminating grid lines on said lm when exposed to X-rays from saidtube and after passing through said grid.

ALFRED SIMON.

